1. Field of the Invention
The invention relates to irrigation systems; and, more particularly, to a method and apparatus for controlling the watering periods of an irrigation system in response to ambient weather conditions.
2. Description of the Prior Art
Various systems have been suggested in the past for providing automatic irrigation control utilizing the various factors that determine the evaporation power of air and thus the loss of vapor from vegetation and soil to effect control of plant irrigation.
For example, U.S. Pat. No. 2,766,070 to Park shows a system having a collector pan for collecting water during sprinkling and turning off the sprinkler system when a predetermined amount of water has been sprinkled. The system automatically turns on again when the water in the collecting pan has evaporated or drained through an adjustable outlet valve. In the Park system, there is no control of the sprinkler system between the "full" and the "empty" condition of the collector pan.
In U.S. Pat. No. 2,776,860 to Griffis, an electronic control is disclosed for a sprinkler system which is operated in response to a collector pan or catcher 11. The presence of water in pan 11 due to rain or sprinkled water is detected and electronically operates an associated sprinkler valve. However, Griffis does not use the pan 11 as an evaporation pan. Graffis uses a funnel for collecting the water and a reservoir for storing it, but the water leaves this reservoir by draining through an adjustable orifice 19 rather than by evaporation. The idea of Griffis system is to respond to the amount of water falling on the ground either through the sprinklers or through rain, but no attempt is made to make it responsive to the amount of water evaporated from an evaporation pan. Further, this type of device would generally be limited to a single valve since it would require a separate system for each valve it operated and thus its cost would be prohibitive in a large scale system. Further, Griffis' system has no control over the time of day the sprinklers would operate.
In a U.S. Pat. No. 2,946,512 to Richards, a system is disclosed which uses an evaporation pan 1 to collect water from a sprinkler and is adapted to close a pair of contacts when a predetermined weight of water has evaporated from the pan. The contacts are opened when a predetermined weight of water is collected in the pan. Again, the system is operative only at the predetermined weights and only a single sprinkler is controlled.
Thus, no prior art system shows a system which uses an evaporation pan to monitor a controller which controls a number of valves which may be operating a number of different types of sprinklers with different precipitation rates and, therefore, different running times.